1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and more particularly to a process for heat treating a semiconductor substrate.
2. Description of the Background Art
In the case where a semiconductor substrate is heat treated by a batch type device, generally, a filling substrate (which will be hereinafter referred to as a dummy substrate) for eliminating a space of a slot to make a heat distribution uniform or a monitor substrate for managing a process is provided directly above upper ends of product substrates disposed in a vertical direction (see Japanese Patent Application Laid-Open No. 2009-117646). For example, a monitor substrate for confirming a thickness of a formed film is provided in a thermal oxidizing step or a CVD (Chemical Vapor Deposition) step in some cases. The same material as that of the product substrate may be used for the dummy substrate or the monitor substrate. In the case where the material of the product substrate is silicon carbide (which will be hereinafter referred to as SiC), however, it is general to use a more inexpensive substrate such as a silicon substrate (which will be hereinafter referred to as Si).
In the case where thermal oxidation for the product substrate having an inorganic film formed on a back face is carried out, a by-product is generated by a reaction to an atmospheric gas over the back face of the dummy substrate if an inorganic film is not formed on the back face. For this reason, there is a problem in that a difference is made in the atmospheric gas to which surfaces of the product substrate disposed directly under the dummy substrate and the other substrates are exposed and different electrical characteristics are thus obtained.